In ink jet printing, printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves projecting a stream of ink droplets to a surface and controlling the direction of the stream, e.g., electronically, so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is well suited for application of characters or decorative marks onto a variety of surfaces including porous and non-porous surfaces.
One of the most common forms of inkjet for marking products in production is CIJ (continuous ink jet) that includes single, multiple, and array-nozzle printers. CIJ printers can deliver a wide range of inkjet ink formulations that serve various industrial applications, particularly coding and marking applications. It is known in the art that current generation CIJ printers must not only solve these application needs but must also meet customer reliability expectations—that is, they must have a high proportion of ‘uptime’ as opposed to periods when they require maintenance such as print head cleaning due to a printer fault or poor print quality. Printers are expected to run without intervention for days or weeks and when typical ink buildup inside the print head results in the need for a print head cleaning, the cleaning process is desirably accomplished by a simple wash-down of the nozzle and other print head components using a cleaning solution.
For high-durability applications where printed images must withstand rigorous adhesion, transfer resistance, and light or heat fastness requirements, pigmented inks are often used. High contrast is also important in these applications. Even though CIJ printers can reliably print pigmented inks, these inks often create the most reliability problems. For example, applications requiring dark contrast (e.g., printing onto light substrates where ink transfer resistance or light fastness is required, such as PVC wire and cables) often use carbon black based inks. Carbon black, however, can be a particularly difficult pigment to use because it may form conductive films on the components in the print head. These films can become more persistently conductive over time, which may eventually negatively impact printer reliability and reduce uptime. Unfortunately, there are no prescriptive methods or readily available materials that can provide inks with dark print contrast, good light stability, good transfer resistance, and the expected level of CU printer reliability.